The present invention relates to the electroplating of metals and, more particularly, to a brightening agent composition for addition to electroplating baths.
The electroplating of substrates such as steel, diecastings, copper and others is a widely accepted method for imparting to the substrates both decorative and functional features. In the decorative aspect, the aim is to provide a lustrous, bright, smooth deposit which is appealing from an appearance viewpoint. Functionally, deposits should be resistant to corrosion and should possess optimum strength, ductility, and other like properties. The best deposits are those which provide a combination of the desired decorative brightness and the desired functional properties.
In the formulation of electroplating baths, the industry has available to it a wide variety of chemicals from which to choose for providing deposits having the desired decorative and functional properties. These chemicals are generally provided singly, or in combination with one or more other chemicals also used in the electroplating bath, in either dry or liquid form, and are mixed with water and other ingredients in appropriate concentrations to form the final electroplating bath. Ideally, all the chemicals or mixtures employed are soluble in water at the concentrations and temperatures employed. In many cases, however, certain of the chemicals, such as those used as brighteners (or grain refining agents as they sometimes are referred to), are not wholly soluble or are completely insoluble in the aqueous plating bath. In these cases, resort has been made in the past to utilization in the bath of materials which assist in the dissolution or substantially uniform dispersion of these chemicals in the bath, such as surfactants, wetting agents or emulsifiers. However, because these chemicals typically are employed in very low concentrations relative to the total bath composition, complete and uniform dispersion of the chemical throughout the bath is essential to attainment of the functional effect sought to be achieved with the chemical. Such dispersion is difficult to attain through mere addition of the chemical per se to the bath. Thus, in some situations, the particular chemical additive preferably is first dissolved in a solvent therefor, or first mixed with an emulsifier or other dispersion-aiding material, prior to admixture of the additive with the remaining components of the plating bath. In these situations, manufacturers of particular additives find it useful to prepackage the additive in admixture with these solubilizing or dispersing materials.
Water-insoluble brighteners and other additives often are packaged in solution with organic solvents such as cellosolves or alcohols (e.g., methanol, isopropyl alcohol), the solutions containing up to about 30% by weight of the brightener. The brightener/solvent mixture is then added to the electroplating bath at levels appropriate to yield a desired concentration of brightener in the bath, typically in the range of about 0.0001 gm/l to about 10 gm/l, the brightener being dispersed in the bath upon addition through the presence in the bath, if required, of various surfactants or wetting agents. Use of brightener/organic solvent mixtures as additives in electroplating baths, however, presents numerous difficulties. For example, the organic solvents generally are highly flammable and care must be taken with respect to handling, shipping and storage of the additive solutions. In addition, the organic solvent may present toxicity problems with respect to its handling. Still further, the use of organic solvents, derived from petroleum feedstocks, raises the cost of the overall brightener additive substantially. Most importantly, use of the brightener additive necessarily results in the addition to the bath of the organic solvent. In order to insure that adverse effects on plating quality and processing conditions do not occur as a result of this addition of organic material, the solvent must be chosen with particular care, and typically only after extensive testing.
It would be particularly useful, therefore, if substantially water-insoluble additives for electroplating baths, such as brighteners, could be provided in prepackaged form along with materials which promote dissolution or dispersion of the additive in the bath, but wherein organic solvents are not required. To be useful as a pre-packaged component for electroplating baths, the additive should be stable in the form in which it is packaged for extended periods of time and under a substantial range of conditions.